The present invention relates to a protection device for controlling the motion of a pneumatic actuator, according to the preamble of claim 1.
Known pneumatic devices used in milking systems for milking an animal, e.g. a cow, suffers from disadvantages in that they do not include any satisfactory additional overload protection against kicks or other not desirable movements of the animal, furthermore they do not include any parallel protection function preventing a fast movement of the actuator in case of a malfunction of the control means comprising servo-pneumatic positioning elements. The known pneumatic devices suffers furthermore from disadvantages in that the protection function is performed in a not sufficiently quick manner. A milking system of this kind is described in for example EP-A-0 360 354.
It is, accordingly, an object of the present invention to overcome the problem of the known devices.
A further object of the invention is to provide a protection for the control of a pneumatic actuator comprising a piston against external accidental influence on the piston movement
This has been solved by a protection device as initially defined, which is characterized in that said control means limits the motion of said piston as soon as signalling from said sensor means indicates that an excessive value of said piston motion has been established.
Hereby is prevented that a fast movement of the piston relatively to the cylinder arises in case of a malfunction or if an animal or a person runs into a robot arm with operating said.
Preferably, a valve means controlled by said control means being connectable to said first and second chambers, and adapted to open a connection between said first and second chambers. Hereby an equalisation of pressure between the first and second chambers is achieved. The piston relatively to the cylinder is therefor flexible due to an external influence.
Suitably, said sensor means comprises a position sensor adapted to sense the position or the relative position per unit of time of said piston in relation to said cylinder, and that said control means is adapted to control said valve means to open in response to a signaling from said position sensor indicating that the value of the position change per unit of time is higher than a predetermined value. Hereby a value of the velocity of said actuator is determined A signal from the control means is given if the value of the motion is exceeded and an equalization of pressure between the first and second chambers is achieved.
Preferably, said sensor means comprises a differential pressure transductor adapted to sense the pressure difference between said first and second chambers, and that said control means is adapted to control said valve means to open in response to a signalling from said transductor indicating that the value of the pressure difference is higher than an estimated pressure composed by a model dependent on the actual control situation of said piston. Hereby an equalization of pressure between said first and second chambers is achieved.
Suitably, said model is derived by means of a Kalmar filter. Hereby is achieved a state, which not will be exceeded
Preferably, said control means is divided into at least one separate control unit controlling the motion of said piston and at least one protective pressure control unit controlling the pressure difference between said first and second chambers, that the signal from said differential pressure tansductor is fed to said protective pressure control unit, that said valve means is controlled by said protective pressure control unit when the pressure difference value sensed by said transductor is higher than an estimated value in dependence on the actual control situation of the piston Hereby an equalization of the pressure between said first and second chambers is achieved even if a malfunction of the control means or the servo valve arises in a situation where an animal or a person runs into the robot arm.
Suitably, for each of said control unit and said protective pressure control unit, the differential pressure is compared with an estimated pressure, which is computed from a model derived by means of the Kalmar filter, and the control signal to said valve means. Hereby either a malfunction in the SW or in the HW do have an effect on the protection function
Preferably, a valve means is associated with said control means, said valve means being connectable to said actuating pressure supply line and to at least one of said first and second chambers, a first valve means is connectable between said valve means and said first chamber, and a second valve means is connectable between said valve means and said second chamber, and a control valve means, connectable to said supply line and associated with said control means, being adapted to control said first and second valve means, and wherein said first and second valve means are in position for normal operation of the device in response to said sensor means, by said excessive value of said piston motion said valve means operates to equalize the pressure between said chambers. Hereby, when a malfunction or an external influence on the actuator arises, the first and second chambers are disconnected from the pressure source, without shutting down the supply line.
Suitably, a first pressure supply line is connectable between said first chamber and said valve means, a second pressure supply line is connectable between said second chamber and said valve means. Hereby the pneumatic pressure may have an effect on the piston relatively to the cylinder in at least one direction.
Preferably, a main valve means is associated with said control means and is connectable to at least one of said first and second chambers and to said actuating supply line. Hereby is achieved that the pressure generation into said device at least can be restrained
Suitably, said robot arm comprises at least one pneumatic actuator for controlling the motion of said robot arm. Hereby is achieved a controllable motion of said robot arm.
Preferably, said robot arm is connected to a robot arm suspension means, which is furthermore hingedly connected to a support means, and said robot arm suspension means being arranged to said support means about an substantially horizontal axis, and at least one of said pneumatic actuators is arranged between said robot arm suspension means and said support means, for allowing said robot suspension means to perform a substantially pendulum movement about said substantially horizontal axis. Hereby is achieved that the arm has good access to e.g. teats and that the risk is less for dirt, such as manure, to hamper the movement of mechanical parts, as the connection between the robot arm suspension means and the support means is arranged at a level substantially above said animal.
Suitably, at least one of said pneumatic actuator is arranged between said robot arm and said support means, for actively moving said robot am in a substantially vertical plane. Hereby is achieved a controllable pendulum movement.
Preferably, said robot arm is pivotally connected to said robot arm suspension means, for allowing said robot arm to perform a pivotal movement in relation to said robot arm suspension means. Hereby is achieved a movability of the robot arm in addition to said pendulum movement.
Suitably, at least one of said pneumatic actuators is arranged between said robot arm and said robot arm suspension means, for actively moving said robot arm in a substantially sideward direction. Hereby is achieved a controllable pivotal movement.
Preferably, said robot arm suspension means comprises a pivot means having a bar movable about a substantially horizontal axis, said bar being provided with a first connection member for said robot arm and a second connection member for said at least one of said pneumatic actuators, each of said first and second connection members being provided with a hinge movable about a substantially vertical axis. Hereby a joint for the pivotal movement is achieved.